Transmission devices are gear trains that convert and transmit the power generated by a power source to comply with the load placed on the output shaft. Many prior art transmission devices, such as those commonly utilized in automobiles, require manual shifting among various gear ratios of the transmission. However, such transmissions are inherently inefficient due both to the loss of momentum caused by the removal of the power in order to change gears, and the inherent difficulty in determining the most efficient response to a load placed upon the output shaft.
A vast array of automatic transmissions are currently available. These transmissions do not require a manual determination of the most efficient response to a load placed upon the output shaft. In addition, they will typically reduce the time required to shift gears and, consequently, reduce the loss of momentum caused by the removal of power. Nonetheless, this loss of momentum, which is inherent in traditional automatic transmissions utilizing a variety of gear ratios, still results in a significant loss of power. In addition, the limited number of gear ratios available prevents these transmissions from achieving maximum efficiency.
In order to avoid momentum losses and attain maximum efficiency, it is desirable for a transmission to have a continuous, infinite range of gear ratios. Such a transmission would not require power to be removed in order to change gears and would be capable of efficiently responding to the various loads placed on the output shaft.
A number of United States Patents disclose continuous, or near-continuous, variable speed transmission. However, each has significant drawbacks. For example, U.S. Pat. No. 1,484,197 discloses a xe2x80x9cchange-speed transmissionxe2x80x9d that includes two conical wheels having teeth of uniform pitch throughout extending along the length of the cone and covering substantially one half of each conical surface. The cones are arranged to mesh with an intermediate wheel and are simultaneously rotated so that the teeth of one conical wheel move out of mesh with the intermediate wheel as the teeth of the other conical wheel move into mesh with the intermediate wheel. The gear ratio is varied by varying the position of the intermediate wheel relatively to the large and small diameters of the conical wheels.
This arrangement is successful at varying the gear ratio without loss of momentum. However, such a system creates inherently high shear stresses that severely limit its useful life. These shear stresses are explained by the fact that the circumference of the cylinder at its front and rear edges is the same, but these circumferences are forced to frictionally and rotatably engage with different-sized same, but these circumferences are forced to frictionally and rotatably engage with different-sized circumferences on the conical surface. As the wider portions of the conical surface travel faster that the narrower portions, the equal circumference of the cylinder respectively engages different-sized circumferences on the conical surface necessarily traveling at different speeds. This causes some portions of the cylinder to slip and rub against the faster conical portions resulting in shear forces.
U.S. Pat. Nos. 2,208,148 and 2,926,538 each describe a xe2x80x9cchange speed gearxe2x80x9d having a plurality of stepped gears arranged side by side on a cone drum and a cylindrical control gear displaceable disposed along a line of the surface of the cone of stepped gears on the driving shaft. Each stepped gear is diametrically subdivided and the two halves of the toothed rim of each step are displaced relative to each other. The spaces between steps are subdivided and staggered and the widths of the spaces is equal to half the width of the teeth of the control gear. The difference in the number of teeth from step to step is divided by two such that the opposite spaces between the points of bisection of the displaced rim halves of all steps are aligned. In operation, the control gear is caused to change its position relative to the cone drum in a synchronized manner such that it moves from one gear to the next in a stepped motion.
As this system utilizes the same cylindrical type control gear as described above, it suffers that same shear stress problems. In addition, the averaged tooth arrangement disclosed in these patents creates both wear and shock on the gears when changing from one set of teeth to another. For this reason, it is useful only at very low speeds.
U.S. Pat. No. 2,234,653 describes a variable transmission having two shafts around which series of teeth are wound. Each series of teeth forms a helix of decreasing diameter, with the teeth of one shaft being aligned with a space between teeth on the other. A spur gear is mounted between the shafts and is dimensioned to engage teeth on both shafts. The movement of the spur gear upward or downward causes it to engage teeth on both shafts, then teeth on only one shaft, and then teeth on both shafts again, with each movement causing an instantaneous change in the gear ratio.
This system does not require power to be removed from the transmission and provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the use of substantially straight teeth causes discontinuous contact between teeth resulting in rapid increases and decreases in stress during gear changes.
U.S. Pat. No. 2,697,365, titled xe2x80x9cPower Transmission Equipmentxe2x80x9d, describes xe2x80x9ca mechanism for producing positive infinitely variable speed changes in a power transmission system.xe2x80x9d The mechanism includes xe2x80x9cat least two conical gear members having uniformly spaced teeth generated in a constant lead spiral path on the conical surface of each of said conical gear members.xe2x80x9d A compensation member, in the form of a spur gear, is interposed between, and engaged with, the conical members such that the axial position of the compensation member with respect to conical gear members determines the speed ratio obtained between the input and output members. In order to vary the speed ratio, the compensation member is disengaged from the conical members.
This system provides the desired variability. However, the cylindrical nature of the spur gear of the compensation member causes it to suffer from the same shear stress problems described above. In addition, the narrow tooth width required by this transmission decreases the overall strength of the teeth.
U.S. Pat. No. 2,875,628 describes a variable speed transmission that utilizes conical gears mounted in opposite relation to each other and each having sets of rigidly attached gear segments bounded by sets that are frictionally engaged with the rigidly attached segments. A spur gear is mounted between, and engaged with, the conical gears. The spur gear is adjustable upward and downward between the conical gears and shift gear ratios by moving from engagement with a rigidly attached gear segment to a frictionally engaged gear segment and then to the next rigidly attached gear segment.
This system is substantially continuous and provides an increased degree of variability. However, the cylindrical nature of the spur gear causes it to suffer from the same shear stress problems described above. Further, the lack of alignment between slopping and non-slipping teeth creates high stresses when going from a slipping portion to an adjacent non-slipping portion.
More recently, U.S. Pat. No. 5,407,399 describes a xe2x80x9cvariable speed friction transmissionxe2x80x9d A variable ratio friction transmission in which a straight sided cone and a roller are in frictional engagement. The roller moves over an element of the cone to change the speed ratio, and at all times stays parallel to itself and moves along a straight line axis. This axis passes through the apex of the cone at all times, but the cone is tilted about its apex to contact the roller or wheel as the ratio is changed.
This system is substantially continues and provides an increased degree of variability. In addition, the frictional engagement of the wheel with the cone eliminates the stress problems encountered with the meshing of spur gears with conical surfaces. However, the frictional engagement of this system severely limits it ability to operate under heavy loads. Further, frictional engagement is prone to wear and, consequently, the frictional surfaces on such a system would need to be replaced regularly.
U.S. Pat. No. 5,425,685 describes a xe2x80x9ccontinuously variable-ratio transmissionxe2x80x9d. This transmission includes a drive shaft having a series of curved teeth that are disposed in the same direction of the shaft and of such a shape that one end has a relatively small diameter and the other a relatively large diameter. A conical gear is engaged with the teeth and is flexibly attached to a splined shaft via a second gear and a universal joint. The splined shaft is attached to a second universal joint to allow it to maintain a constant angle relative to the surface of the shaft, allowing the conical gear to conform to the angle of the surface of the teeth formed on the shaft. In operation, the speed is changed by moving the conical gear up and back along the surface of the drive shaft.
This system is also substantially continues and provides an increased degree of variability. However, it also relies upon frictional engagement, severely limiting its ability to operate under heavy loads and making it prone to wear.
U.S. Pat. No. 5,545,101 describes a xe2x80x9cfriction type continuously variable transmissionxe2x80x9d in which a planetary gear unit is attached to a frictionally engaged continuously variable unit. The planetary gear unit has a drive shaft, a carrier fixed to the drive shaft, a plurality of planetary gears supported on the carrier, and an internal gear meshing with the planetary gears. The continuously variable transmission unit has an input shaft to which is fixed to a sun gear meshing with the planetary gear.
This system is substantially continuos and provides an increased degree of variability. In addition, the frictional engagement of the wheel with the cone eliminates the stress problems encountered with the meshing of spur gears with conical surfaces. Finally, the integration of the planetary system allows the impeller to be rotated at a high speed even if the speed ratio of the continuously variable transmission unit is low. However, it is not without its drawbacks. As with all frictional systems, the frictional engagement of this system severely limits it ability to operate under heavy loads. Further, frictional engagement is prone to wear and, consequently, the frictional surfaces on such a system would need to be replaced regularly.
U.S. Pat. No. 5,601,509 describes a xe2x80x9ctaper roller continuously variable transmissionxe2x80x9d that includes a set of power input cones tapered in a first direction and a set of power output cones tapered in a opposite direction. Each cone has an axis of rotation oriented such that a portion of a surface parallel to a portion of the surface of each of the other cones in the same set. A power transfer ring tractionally engages the sets of cones on the parallel portions to transfer power from the input to the output set of cones. The power transfer ring is movable axially along the parallel portions to vary the speed ratio from the power input cones to the power output cones.
This system is also substantially continues and provides an increased degree of variability. However, it again relies upon frictional engagement, severely limiting its ability to operate under heavy loads and making it prone to wear.
The present invention is a transmission apparatus, transmission system, and method for varying a speed of an output shaft. In its most basic form, the transmission apparatus includes a pinion gear having a plurality of helical teeth. A cone is disposed in contact with said pinion gear and includes a plurality of conic teeth and a plurality of scaling teeth. The conic teeth are arranged about the cone to form a plurality of conic rings disposed about a plurality of nascention circles on the cone. The conic teeth of the conic rings are dimensioned to mate with the helical teeth of the pinion gear such that the conic teeth neutralize a change in surface speed of the cone along the conic teeth. The scaling teeth form at least one acceleration channel and at least one deceleration channel extending from each of the conic rings and intercepting an adjacent conic ring. The acceleration channel and deceleration channel are disposed along a nascention offset line between nascention circles of adjacent conic rings.
In operation, the pinion gear moves about a given conic ring at a substantially constant speed until a higher or lower speed is desired. If a higher speed is desired, the pinion gear is moved into an acceleration channel, which allows the gear to move to a higher conic ring. If a lower speed is desired, the pinion gear is moved into a deceleration channel, which allows the gear to move to a lower conic ring.
In the preferred transmission apparatus, the acceleration channel includes an acceleration channel entrance, an acceleration tube, and an acceleration channel exit, and the deceleration channel includes a deceleration channel entrance, a deceleration tube, and a deceleration channel exit. In this preferred embodiment, the acceleration channel entrance of one acceleration channel and the deceleration channel exit of one deceleration channel overlap along a bottom landing made up of the conic teeth of one of the rings. Likewise The deceleration channel entrance of one deceleration channel and the acceleration channel exit of one acceleration channel overlap along a top landing, the top landing comprising conic teeth of another of the rings. In embodiments utilizing stepped scaling teeth, a plurality of tapered spaces are disposed between the scaling teeth and a pitch line of each scaling tooth is varied dependent upon a migration of nascention coordinates of the scaling teeth on the nascention-offset line. However, in the preferred embodiment, the scaling teeth are substantially continuous, and the pitch line is based upon a migration of the nascention coefficients between conic rings. Finally, the conic teeth of the preferred apparatus are dimensioned to form a plurality of spaces having an involute profile.
The system of the present invention includes the apparatus of the present invention, a splined power output shaft attached to the pinion gear, a power input shaft attached to the cone, and a motion control device in communication with the pinion gear and dimensioned to move the pinion gear along said splined power output shaft. In the preferred system, the motion control device includes a control yoke movably attached to the threaded shaft, a control motor for rotating the threaded shaft, and a microprocessor for controlling the control motor. A rotational encoder is provided to determine a degree of rotation of said cone from a zero point, a lateral sensor is provided to encode a lateral location of said pinion gear, and a load sensor is provided for sensing an amount of torque on the system. Finally, the microprocessor includes an algorithm for accepting inputs from the rotational encoder, the lateral sensor and the load sensor and calculating a translocation speed based upon said inputs.
Therefore, it is an aspect of the invention to provide a transmission that avoids momentum losses by not requiring power to be removed in order to change speed.
It is an aspect of the invention to provide a transmission that has an infinite range of gear ratios.
It is an aspect of the invention to provide a transmission that is capable of efficiently responding to the various loads placed on the output shaft.
It is an aspect of the invention to provide a transmission that avoids the shear stress problem attendant to the use of cylindrical spur gears in contact with conical gears.
It is an aspect of the invention to provide a transmission in which the arrangement of rings prevents excessive sliding within the gears.
These aspects of the invention are not meant to be exclusive and other features, aspects, and advantages of the present invention will be readily apparent to those of ordinary skill in the art when read in conjunction with the following description, appended claims and accompanying drawings.